Sudden, unexpected loading to the spine results in the most severe and costly back injuries. Fast and appropriate postural control responses during these sudden, unexpected events are important to spare the spine from harmful loading. Unfortunately, people with low back pain (LBP) have impaired postural control, which suggests that they are more likely to re-injure themselves and develop chronic back pain. Experimental and modeling work has demonstrated that poor postural control found in the LBP group, in part, can be explained by longer delays in postural responses. There are several studies documenting an increase in the postural response times associated with back pain. In addition, there are studies documenting increased variability in postural responses suggesting that postural control is less precise. We hypothesize that if osteopathic manipulative therapy (OMT) can effectively reduce somatic dysfunction and pain, then improvements in postural control, including faster and more accurate responses, should be realized. This improvement in postural control should then mitigate any adverse effects from a sudden, unexpected event. To test this hypothesis, we will develop objective performance measures of the postural control system, in particular assessment of the bandwidth of control (speed of the control system) and accuracy (error between desired and actual output). This will be accomplished with three specific aims: (1) to compare postural control in healthy and LBP individuals;(2) to compare postural control in LBP individuals before and after OMT;and (3) to classify subjects into homogeneous groups of measures of somatic dysfunction and postural control, and to evaluate group differences in terms of pain and disability. Both position and force control will be assessed during tracking and stabilization tasks. In addition, a simulated lifting task will be used to assess the response of the postural control system to sudden, unexpected perturbations from shifting the base of support. The proposed research will apply an innovative approach, based on Systems Science, to develop sensitive and objective clinical research tools that can assess performance changes in the postural control system.